When Knowledge Counts Twice: The Role of Turnout in EU Referendums

Aggregate data on EU referendums indicate that turnout has a significant impact on the referendum outcome. Existing studies of referendums, however, tend to either explain turnout, or, given a vote and ignoring non-voters, vote choice. It therefore misses an important part of citizens’ choice, namely the impact of vote preference on turnout. This is problematic especially when individuals’ characteristics influence both the decision to turn out and the vote choice of those who decide to vote. For instance, voters who are more knowledgeable about the referendum issue are more likely to turn out as well as to vote “Yes” when they do. This means that there is an amplified effect of knowledge on voting behaviour, first via turnout and second via vote choice. This paper proposes a new formal model to capture the interaction between uncertainty, turnout, and vote choice. In particular, it develops a game-theoretical model of the impact of uncertainty around the referendum options on the decision to participate and the support for the referendum question – in this case further European integration. We develop an accompanying statistical model that reflects the formal model and jointly estimates turnout, vote choice, and their interaction. We evaluate the performance of the model on survey data on a series of ten European integration referendums over the past 25 years, in Denmark, Ireland, France, Luxembourg, The Netherlands, and Spain. We show that the estimated effect of uncertainty – or lack of knowledge – on referendum outcomes is significantly larger when the relevance of this variable for both turnout and vote choice is considered simultaneously.